header {
    display: block;
    margin: 0 auto;
    width: 100%;
    text-align: center;
}

header h1 {
    font-family: Arial;
    font-size: 60px;
    font-weight: bold;
    margin: 0 auto;
}

header #new_game_button {
    display: block;
    margin: 0px auto;
    width: 100px;
    padding: 10px 10px;
    background-color: #8f7a66;
    font-family: Arial;
    color: white;
    border-radius: 10px;
    text-decoration: none;
}

header #new_game_button:hover {
    background-color: #9f8b77;
}

header p {
    font-family: Arial;
    font-size: 25px;
    margin:5px auto;
}

#grid_container {
    width: 460px;
    height: 460px;
    padding: 20px;
    margin: 0px auto;
    background-color: #bbada0;
    border-radius: 10px;
    position: relative;
}

.grid_cell {
    width: 100px;
    height: 100px;
    border-radius: 6px;
    background-color: #ccc0b3;
    position: absolute;
}

.number_cell {
    border-radius: 6px;
    font-family: Arial;
    font-weight: bold;
    font-size: 60px;
    line-height: 100px;
    text-align: center;
    position: absolute;
}